Woolly mammoths were breastfed for far, far longer than any of their modern counterparts, sometimes going three years before eating solid food. This ancient parenting choice might ultimately have driven mammoths to extinction.

Researchers examined the teeth from baby and adult mammoths who once lived in Old Crow, Yukon. They discovered that mammoths didn't start eating solid foods until very late in life - at least as late as two years old, and perhaps not until they were three. Modern elephants, on the other hand, wean their children relatively soon after birth. So why the big delay?

University of Western Ontario researcher Jessica Metcalfe explains that there just weren't enough food sources to support young mammoths any earlier than that, although predators like the saber-toothed tiger might have played a role as well:

"In modern Africa, lions can hunt baby elephants but not adults. They can't kill adults. But they can kill babies and by and large, they tend to be successful when they hunt at night because they have adapted night vision. In Old Crow, where you have long, long hours of darkness, the infants are going to be more vulnerable, so the mothers nursed longer to keep them close."

But keeping young mammoths on breast milk alone would have had its costs for the mothers. In fact, Metcalfe suspects that having to constantly lactate taxed mammoth females beyond their biological capabilities, and might well have played a role in driving them to extinction:

"Today, a leading cause of infant elephant deaths in Myanmar is insufficient maternal milk production. Woolly mammoths may have been more vulnerable to the effects of climate change and human hunting than modern elephants not only because of their harsher environment, but also because of the metabolic demands of lactation and prolonged nursing, especially during the longer winter months."

Mammoths only died out less than 10,000 years ago, but their species lived on this planet for millions of years, which makes their extinction incredibly recent in geological terms. Ancient climate change likely played a big role in killing off the mammoths, and Metcalfe believes they offer a perfect case study in how animals can adapt - or, ultimately, fail to adapt - to rapidly changing climate conditions:

"Mammoths lived all over the world for thousands of years, even millions of years, and then became extinct about 10,000 years ago, which was around the time the climate started warming the last time. Understanding their ecology, their adaptations and their behaviour not only gives us insight into why they became extinct but also, potentially, gives us a better understanding of modern day mammals and how they might respond to the current warming of the planet."